Micro transducer molding

ABSTRACT

Articles and methods are provided for miniature acoustic transducers having highly compliant suspension systems despite their small size. In various examples the suspension system is molded of a liquid silicone rubber (LSR) and is molded in an interior cavity geometry that includes and apex radially offset and/or axially offset from a desired cured position of an apex of the suspension.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/207,083, filed on Mar. 19, 2021, titled MICRO TRANSDUCER MOLDING,which further claimed the benefit of provisional U.S. Patent ApplicationSer. No. 62/992,583, filed on Mar. 20, 2020, titled MICRO TRANSDUCERMOLDING, the contents of each of which is incorporated herein in theirentirety for all purposes.

BACKGROUND

This disclosure relates to an electro-acoustic transducer, and invarious examples relates to a miniature electro-acoustic transducerincluding a diaphragm having a compliant suspension/surround.

SUMMARY

Systems and methods disclosed herein are directed to miniatureelectro-acoustic transducers having small diaphragms, such as thosehaving diameters of 8.0 mm or less, diameters of 5.5 mm or less, ordiameters of 4.2 mm or less, in various examples, suspended byhigh-compliance suspension systems. The suspension system may be asurround formed of a highly compliant material that may be injectionmolded to attach or suspend the diaphragm within a frame. In someexamples, an overall width of miniature electro-acoustic transducers,e.g., a width of the frame, in accord with those herein may be 3.0 mm orless, may be 4.2 mm or less, 5.5 mm or less, or 8.0 mm or less.

According to various examples, diaphragms in accord with those hereinmay be comprised of a central piston, the suspension, and the frame. Insome examples, the central piston and/or the frame may be constructed ofa thermoplastic materials, such as a Nylon and/or Glass Fibercombination. In some examples, either of the frame or the piston may beconstructed of Nylon 9T (a.k.a. Polyamide 9T).

In various examples, the suspension (also called a surround) may beformed of a liquid silicone rubber (LSR), or other suitably compliantmaterial, of durometer less than 70 shore A, and preferably less than 50Shore A. In some examples, the durometer of the surround material may bebetween 20 Shore A and 40 Shore A, and in certain examples may be about30 Shore A.

In various examples, a thickness of the surround material may be in arange of 10 to 100 μm, and may be less than 50 μm, and in some examplesmay be in the range of 20-30 μm, and in certain examples may be about 25μm. In various examples, the diaphragm may be 5.5 mm or less indiameter, and in some examples may be about 5.2 mm or less, and incertain examples may be about 4 mm or less. In various examples, thesuspension may result in the piston and suspension assembly having anaxial stiffness at a rest position of 50 N/m or less. In some examplesthe axial stiffness may be 35 N/m or less, and in certain examples maybe 25 N/m or less. In certain examples the axial stiffness may be in therange of about 8-30 N/m or may be in the range of about 5-15 N/m. Byaxial stiffness is meant an amount of force required to move the pistonaxially, e.g., perpendicular to a surface of the piston and/orperpendicular to a plane of the surround, an amount of distance from arest position. This axial stiffness may increase as the piston movesfurther from the rest position, but references to axial stiffness hereinrefer to the force-to-distance ratio at or very near the rest position,e.g., before excursion away from the rest position increases the forcerequired, such as excursion amounts that do not stretch the suspensionsystem, for example.

According to various aspects, a method of forming an acoustic transduceris provided that includes providing a mold having an interior cavitygeometry with at least one of a radial offset or an axial offset from adesired geometry of the suspension and injecting a compliant materialinto the mold.

Various examples also include providing a piston at a first positionrelative to the mold, providing a frame at a second position relative tothe mold, and wherein injecting the compliant material into the moldcauses the compliant material to contact each of the piston and theframe. In some examples, the compliant material at least partiallyadheres to each of the piston and the frame, such that upon removal fromthe mold the compliant material suspends the piston relative to theframe.

According to some examples, an outer edge of the interior cavitygeometry of the mold defines a geometrically closed shape having alargest linear dimension less than 8 millimeters. In various examplesthe largest linear dimension is 5.5 mm or less. In various examples thegeometrically closed shape may be a circle.

In certain examples at least one of the radial offset is in a range ofabout 20 micrometers (μm) to 110 μm and the axial offset is in a rangeof about 20 μm to 130 μm.

According to other aspects, an acoustic transducer is provided thatincludes a frame having a largest linear dimension of 8.0 millimeters orless, a suspension formed of a compliant material coupled to the frame,and a piston coupled to and suspended by the suspension, such that thepiston is suspended within the frame and the piston when in an at-restposition reacts to an applied force with a stiffness in a range of 5 to50 Newtons per meter (N/m).

According to some examples, the suspension may be formed by providing amold having an interior cavity geometry with at least one of a radialoffset or an axial offset from a desired geometry of the suspension andinjecting the compliant material into the mold.

According to various examples, injecting the compliant material into themold causes the compliant material to contact each of the piston and theframe.

In certain examples, the compliant material at least partially adheresto each of the piston and the frame, such that upon removal from themold the compliant material suspends the piston relative to the frame.

In some examples, an outer edge of the interior cavity geometry of themold defines a geometrically closed shape having a largest lineardimension of 5.5 millimeters or less. In certain examples thegeometrically closed shape may be a circle.

According to certain examples, at least one of the radial offset is in arange of about 20 micrometers (μm) to 110 μm and the axial offset is ina range of about 20 μm to 130 μm.

According to another aspect, a mold is provided that includes aninterior cavity having an interior geometry including at least one of aradial offset or an axial offset from a desired geometry of a transducersuspension, and an inlet to allow a compliant material to be injected inthe interior cavity.

According to some examples, at least one of the radial offset is in arange of about 20 micrometers (μm) to 110 μm and the axial offset is ina range of about 20 μm to 130 μm.

According to various examples, an outer edge of the interior geometry ofthe mold defines a geometrically closed shape having a largest lineardimension of 8.0 millimeters or less. In certain examples thegeometrically closed shape may be a circle.

In various examples, the mold includes one or more allowances to engageat least one of a piston and a frame such that the compliant material,when injected in the interior cavity, contacts the at least one of thepiston and the frame. In certain examples the compliant material atleast partially adheres to each of the at least one of the piston andthe frame, such that upon removal from the mold the compliant materialsuspends the piston relative to the frame.

Still other aspects, examples, and advantages of these exemplary aspectsand examples are discussed in detail below. Examples disclosed hereinmay be combined with other examples in any manner consistent with atleast one of the principles disclosed herein, and references to “anexample,” “some examples,” “an alternate example,” “various examples,”“one example” or the like are not necessarily mutually exclusive and areintended to indicate that a particular feature, structure, orcharacteristic described may be included in at least one example. Theappearances of such terms herein are not necessarily all referring tothe same example.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one example are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and examples, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the inventions. In thefigures, identical or nearly identical components illustrated in variousfigures may be represented by a like reference character or numeral. Forpurposes of clarity, not every component may be labeled in every figure.In the figures:

FIG. 1 is a schematic diagram of an example miniature transducer inaccord with examples described herein;

FIG. 2A is a schematic diagram illustrating an example surroundcomponent of the miniature transducer of FIG. 1 ; and

FIG. 2B is a schematic diagram illustrating an example mold geometry toproduce the example surround component of FIG. 2A.

DETAILED DESCRIPTION

Modern in-ear headphones, or earbuds, typically include microspeakers,which are miniature electro-acoustic transducers. A microspeaker mayinclude a voice coil positioned in a magnetic field and mechanicallycoupled to an acoustic diaphragm. An electrical signal provided to thevoice coil results in motion of the diaphragm—and a piston oracoustically radiating surface thereof—thereby generating an acousticsignal responsive to the electrical signal. The microspeaker may includea frame from which the piston is suspended by a suspension or surround,and may include a housing that encloses the voice coil and a magneticstructure or circuit. As the size of earbuds decrease, it becomesincreasingly difficult to fabricate an acoustic diaphragm with asurround suspension in a manner that allows broad spectrum coverage.Examples of microspeakers described herein include a highly compliant(low stiffness) surround or suspension, as compared to conventionalmicrospeakers. At least one benefit of such high-compliance transducersincludes broader spectral output than conventional microspeakers, e.g.,higher acoustic displacement and output power across a larger range offrequencies as compared to conventional designs.

In general, in one aspect, an electro-acoustic transducer includes apiston having a front surface, a back surface, and a perimeter; a bobbincoupled to the piston; and a suspension (surround) coupled to the pistonand frame. The bobbin may be configured to hold a winding of anelectrical conductor (e.g., a voice coil). A motion of the bobbin alongthe bobbin axis generates a movement of the piston to thereby generatean acoustic signal that propagates from the front surface of the piston.In some examples, the voice coil may be more directly coupled to thepiston, without a bobbin. The suspension provides a high compliancegiven the overall dimensional scale of the transducer. In someinstances, the term diaphragm may be intended to refer to the pistonand/or the overall acoustically radiating surface (such as may includethe front surface of the piston and a portion of the suspension). Inother instances, the term diaphragm may be intended to refer to adiaphragm assembly comprised of the piston, surround, and frame.

Examples of the methods and apparatuses discussed herein are not limitedin application to the details of construction and the arrangement ofcomponents set forth in the following description or illustrated in theaccompanying drawings. The methods and apparatuses are capable ofimplementation in other examples and of being practiced or of beingcarried out in various ways. Examples of specific implementations areprovided herein for illustrative purposes only and are not intended tobe limiting. In particular, functions, component, elements, and featuresdiscussed in connection with any one or more examples are not intendedto be excluded from a similar role in any other examples.

Examples disclosed herein may be combined with outer examples in anymanner consistent with at least one of the principles disclosed herein,and references to “an example,” “some examples,” “an alternate example,”“various examples,” “one example” or the like are not necessarilymutually exclusive and are intended to indicate that a particularfeature, structure, or characteristic described may be included in atleast one example.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. Any references toexamples, components, elements, acts, or functions of the systems andmethods herein referred to in the singular may also embrace embodimentsincluding a plurality, and any references in plural to any example,component, element, act, or function herein may also embrace examplesincluding only a singularity. Accordingly, references in the singular orplural form are not intended to limit the presently disclosed systems ormethods, their components, acts, or elements. The use herein of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.Any references to front and back, left and right, top and bottom, upperand lower, and vertical and horizontal are intended for convenience ofdescription, not to limit the present systems and methods or theircomponents to any one positional or spatial orientation.

FIG. 1 illustrates an example transducer 100 in cross-sectional viewhaving a piston 110 supported by a suspension 120 that is furthercoupled to a frame 130. The frame 130 forms a support structure in whichthe piston 110 is suspended by the suspension 120. In various examples,the frame 130 may be coupled to a cup 140, which in combination with theframe 130, suspension 120, and piston 110 may form an enclosed volume.Further in various examples, a bobbin 150 may be mechanically coupled tothe piston 110 and may support a voice coil 160. The voice coil 160 maybe positioned in a magnetic field that may be created by a primarymagnet 170 in some examples. When electrical current is passed throughthe voice coil 160, it generates a further magnetic field that interactswith the magnetic field of the primary magnet 170 and creates a force inan axial direction, A, that is passed via the bobbin 150 to the piston110, which moves in response and thereby converts electrical energy intoacoustic energy in the air, as known in the art. In some but not allexamples, the magnetic field may be further shaped and/or strengthenedby a secondary magnet 180 and/or a coin 190. The structure of theillustrated example transducer 100 is merely an example and numerousother structures may be suitable without departing from the inventivesystems and methods described herein.

Methods and apparatuses described herein are directed to the manufactureand form of the suspension 120. The piston 110 and the frame 130 formthe immediate environment of the suspension 120 and may take any ofnumerous forms. The combination of a piston 110, the suspension 120, andthe frame 130 may be referred to herein as an assembly or a diaphragm(or a diaphragm assembly). The suspension 120 allows the piston 110 tomove in response to force from the voice coil 160. The amount of forcerequired to move the piston 110 a given distance in the axial direction,A, from a nominal or at-rest position, is a stiffness of the suspension120 (or of the assembly). In various examples, the axial stiffness maybe 50 Newtons per meter (N/m) or less. In some examples, the axialstiffness may be 35 N/m or less or may be 25 N/m or less. In certainexamples the axial stiffness may be in a range of about 8-30 N/m or maybe in a range of about 5-15 N/m.

In various examples, the transducers described herein may have a totaldiameter, D, (or in some cases a diaphragm diameter) of 8.0 millimeters(mm) or less, 5.5 mm or less, and in certain examples may be about 4 mmor less.

While the piston 110 is shown as a curved or dome structure, in variousexamples, the piston 110 may be a substantially planar structure.Additionally, the piston 110, as illustrated, is a rigid structurehaving an exposed outer or front surface. The front surface is the airinterface from which acoustic energy is emitted in operation. Ingeneral, the term diaphragm may refer to that portion of a transducer incontact with a fluid, e.g., air, that moves against the fluid causingpressure waves to be generated in the fluid. In various examples, thepiston 110 as illustrated may be covered or coated in another material,and the face of such material may technically be the ‘diaphragm’ by theabove definition, without departing from the examples described herein.For example, in some instances, the material from which the suspension120 is formed may extend over the surface of the piston 110.

While FIG. 1 illustrates a bobbin 150, various examples may not includea bobbin and may have alternate forms of coupling the voice coil 160 tothe piston 110 or the diaphragm assembly.

In various examples, the suspension 120 is formed of a soft compliantmaterial. In various examples, the suspension material may be between 20Shore A and 40 Shore A, and in certain examples may be about 30 Shore A.

FIG. 2A illustrates a close-up cross-sectional view of the assembly ofthe piston 110, suspension 120, and frame 130. The suspension 120 has athickness 122 that may be in a range of 10 to 100 micrometers (μm), andmay be less than 70 μm or less than 50 μm, and in various examples maybe less than 40 μm, and in some examples may be in the range of 20-30μm, and in certain examples may be about 25 μm.

In certain examples, the suspension 120 may be formed by injectionmolding. In various examples, the suspension 120 may be formed fromliquid silicone rubber (LSR) or other suitable compliant material. Suchmaterials, including LSR, may shrink during curing. At the scale orphysical size of the miniature transducers and compliant suspensionmaterials as described herein, the suspension 120 may shrink in variousnon-proportional manners. Accordingly, the forming of the suspension 120in accord with methods and examples described herein accommodatesnon-proportional shrinkage of the compliant material of the suspension120 at the physical dimensions of the suspension 120. Accordingly, amold cavity 200 is illustrated in FIG. 2B from which the examplesuspension 120 may be produced. The mold cavity 200 has an interiorgeometry that matches a shape of the pre-cured suspension material to beformed, such that a properly shaped suspension 120 will result aftercuring, drying, shrinking, etc.

FIG. 2A includes two reference positions defined by the intendedresulting shape of the suspension 120, an apex 124 at the highest pointof a “half-roll” of the suspension 120 and a reference 126 at anarbitrary axial position. The mold cavity 200 is shaped such that one ormore of these positions are at different locations than the resultingsuspension 120. It should be noted that the term “half-roll” isprimarily intended to refer to a non-planar (e.g., non-flat) shape ofthe suspension 120 and is not intended to mean that the resulting shapenecessarily has a semi-circular cross-section.

In various examples, the interior geometry of the mold cavity 200 has anapex having a radial offset 224 from the apex 124 of the suspension 120.In certain examples, the offset 224 may be such that the apex of themold cavity 200 is closer to the piston 110, e.g., closer to the centerof the transducer, than the apex 124.

In some examples, the radial offset 224 may be 10 μm or greater. In someexamples the radial offset 224 may be in a range of about 20 μm to 60μm. In some examples the radial offset 224 may be in a range of about 20μm to 130 μm. In certain examples, the radial offset 224 may be about 40μm, 70 μm, or 110 μm. In various examples, the radial offset 224 mayrepresent a shift of the mold apex (relative to the apex 124 of theresulting suspension 120) defined as a fraction or percentage of a span128 (or gap) over which the suspension 120 extends. In various examplesthe radial offset 224 may be 5% to 30% of the span 128. In some examplesthe radial offset 224 may be 18% to 30% of the span 128.

In various examples, the span 128 may be about 500 μm or less. In someexamples, the span 128 may be about 430 μm or less. In some examples,the span 128 may be a fraction of the diameter, D, of FIG. 1 , of about5-15%. In certain examples, the span 128 may be about 7 to 13% of thediameter, D, and in more specific examples the span 128 may be 8 to 12%of the diameter, D.

In various examples, the interior geometry of the mold cavity 200includes an axial offset 226 such that while molding the suspension 120,the piston 110 is held in a position axially offset from its at-restposition (e.g., relative to the frame 130). In various examples, theaxial offset 226 may be 25 μm or greater. In some examples the axialoffset 226 may be in a range of about 50 μm to 130 μm. In certainexamples, the axial offset 226 may be in a range of about 70 μm to 120μm. According to some aspects, various examples may have an axial offset226 of 20 μm to 60 μm, or 30 μm to 60 μm, and may be in a range of 40 to50 μm. In certain examples, the suspension 120 of a miniature transducerhaving diameter, D, of about 4.2 mm may be manufactured by a mold cavity200 having an axial offset of about 40 to 50 μm.

After molding according to the mold cavity 200 as described herein, theresulting suspension 120 after shrinking from the mold may have adesired shape, e.g., according to FIG. 1 and as further illustrated inFIG. 2A. While not expressly shown in the figures, the mold cavity 200may include an inlet or nozzle through which the compliant material maybe introduced or injected into the mold cavity 200.

Having described above several aspects of at least one example, it is tobe appreciated various alternations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only, and the scope of the invention should be determined fromproper construction of the appended claims and their equivalents.

What is claimed is:
 1. An acoustic transducer comprising: a frame havinga diameter of 8.0 millimeters or less; a non-planar suspension formed ofa compliant material coupled to the frame, the suspension being formedby injecting the compliant material into a mold having an interiorcavity geometry with an apex positioned to be radially offset or axiallyoffset from a desired cured position of the apex of the suspension; anda diaphragm coupled to and suspended by the suspension, such that thepiston is suspended within the frame
 2. The acoustic transducer of claim1 wherein the suspension provides a stiffness such that the diaphragmreacts to an applied force in a range of 5 to 50 Newtons per meter(N/m).
 3. The acoustic transducer of claim 1 wherein the suspensionprovides a stiffness such that the diaphragm reacts to an applied forceby 35 N/m or less.
 4. The acoustic transducer of claim 1 wherein thesuspension provides a stiffness such that the diaphragm reacts to anapplied force by 25 N/m or less.
 5. The acoustic transducer of claim 1wherein the compliant material at least partially adheres to each of thediaphragm and the frame and is formed by providing the diaphragm at afirst position relative to the mold, providing the frame at a secondposition relative to the mold, and injecting the compliant material intothe mold, causing the compliant material to contact each of thediaphragm and the frame.
 6. The acoustic transducer of claim 1 whereinthe diameter is 5.5 mm or less.
 7. The acoustic transducer of claim 1wherein the diameter is 4.2 mm or less.
 8. The acoustic transducer ofclaim 3 wherein the diameter is 5.5 mm or less.
 9. The acoustictransducer of claim 4 wherein the diameter is 4.2 mm or less.
 10. Theacoustic transducer of claim 1 wherein at least one of the radial offsetis in a range of about 20 micrometers (μm) to 110 μm or the axial offsetis in a range of about 20 μm to 130 μm.
 11. An acoustic transducercomprising: a circular frame having a diameter of 8.0 millimeters orless; a half-roll suspension having a substantially semi-circularcross-section formed of a compliant material coupled to the frame, thesuspension being formed by injecting the compliant material into a moldhaving an interior cavity geometry with an apex positioned to beradially offset or axially offset from a desired cured position of theapex of the suspension; and a diaphragm coupled to and suspended by thesuspension, such that the piston is suspended within the frame
 12. Theacoustic transducer of claim 11 wherein the suspension provides astiffness such that the diaphragm reacts to an applied force in a rangeof 5 to 50 Newtons per meter (N/m).
 13. The acoustic transducer of claim11 wherein the suspension provides a stiffness such that the diaphragmreacts to an applied force by 35 N/m or less.
 14. The acoustictransducer of claim 11 wherein the suspension provides a stiffness suchthat the diaphragm reacts to an applied force by 25 N/m or less.
 15. Theacoustic transducer of claim 11 wherein the compliant material at leastpartially adheres to each of the diaphragm and the frame and is formedby providing the diaphragm at a first position relative to the mold,providing the frame at a second position relative to the mold, andinjecting the compliant material into the mold, causing the compliantmaterial to contact each of the diaphragm and the frame.
 16. Theacoustic transducer of claim 11 wherein the diameter is 5.5 mm or less.17. The acoustic transducer of claim 11 wherein the diameter is 4.2 mmor less.
 18. The acoustic transducer of claim 13 wherein the diameter is5.5 mm or less.
 19. The acoustic transducer of claim 14 wherein thediameter is 4.2 mm or less.
 20. The acoustic transducer of claim 11wherein at least one of the radial offset is in a range of about 20micrometers (μm) to 110 μm or the axial offset is in a range of about 20μm to 130 μm.